This invention relates to photolithography. More particularly, it relates to line width control in a photolithography device.
Lithography is used in the manufacture of semiconductor chips. Lithography, or more particularly photolithography, involves projecting one or more images of a reticle or semiconductor circuit mask onto a photosensitive substrate of a wafer. The wafer is then processed to form one or more circuits. As the art of semiconductor chip manufacturing progresses and the size of semiconductor devices become smaller, there is a need for improving line width control in photolithography devices.
Large semiconductor chips are typically manufactured using a step-and scan lithography device. A step-and-scan lithography device operates by scanning a typically rectangular illumination field defined by an illumination system over a reticle having a circuit pattern thereon. A step-and-scan lithography device is used to manufacture large semiconductor chips, in part, because the size of a semiconductor chip that can be manufactured using a step-and-scan lithography device is not limited to the size of the device""s projection optics.
A method and system for improving line width control, for example, in a step-and-scan lithography device, is described by McCullough et al. in U.S. application Ser. No. 09/599,383, filed Jun. 22, 2000, xe2x80x9cIllumination System With Spatially Controllable Partial Coherence Compensating For Linewidth Variances In A Photolithography System,xe2x80x9d which is incorporated in its entirety herein by reference. McCullough et al. describe using a custom-designed optical element, such as a microlens array or a diffractive optical element, to control the partial coherence of an illumination system of a lithography device and thereby compensate for line width variances in the lithography device. The custom-designed optical element described by McCullough et al. is designed to compensate for predetermined horizontal and vertical biases associated with a particular lithography device. A limitation of the method of McCullough et al., however, is that it is typically an expensive and time-consuming process to design and manufacture the custom-designed optical element described by McCullough et al. Thus, the custom-designed optical element described by McCullough et al. cannot be readily adjusted, for example, as the horizontal and vertical biases associated with a particular lithography device change with time.
Other types of lithography devices such as step-and-repeat lithography devices and field-stitching lithography devices also exhibit horizontal and vertical biases that cause line width variances. Compensating for the horizontal and vertical biases in these lithography devices and improving line width control is just as important as compensating for horizontal and vertical biases and improving line width control in a step-and-scan lithography device.
What is needed is a system and method for controlling line width variations in a lithography device that overcomes the limitations described above.
The present invention provides a system and method for controlling line width variances in a lithography device. Electromagnetic energy is emitted from an illumination source. A portion of the emitted electromagnetic energy passes through an illumination optics module. The illumination optics module includes a partial coherence adjuster module having a first and a second optical element. These two optical elements are used together to vary the partial coherence of electromagnetic energy emitted by the illumination source, as a function of illumination field position. These two optical elements thereby control line width variances, including time varying variances, in the lithography device.
In an embodiment, the lithography device includes a reticle stage, a projection optics module, and a wafer stage. The reticle stage is positioned adjacent to the illumination optics module such that electromagnetic energy exiting the illumination optics module will illuminate a portion of a reticle held by the reticle stage. The projection optics module is optically located between the reticle stage and the wafer stage. Electromagnetic energy passing through a reticle held by the reticle stage will enter the projection optics module and be imaged by the projection optics module on a photosensitive substrate, such as a wafer held by the wafer stage.
In an embodiment, the first optical element is a standard optical element designed to compensate for horizontal and vertical biases associated with lithography devices of a particular make and model. This standard optical element is not customized based on the horizontal and vertical biases associated with a particular lithography device. The second optical element is used for making any changes in the angular distribution of electromagnetic energy incident upon the first optical element needed to compensate for horizontal and vertical biases associated with a particular lithography device.
In another embodiment, the first optical element is a custom optical element designed to compensate for predetermined horizontal and vertical biases associated with a particular lithography device. This custom optical element is not intended to be interchangeable in other lithography devices. In this embodiment, the second optical element is used for making relatively minor changes in the angular distribution of electromagnetic energy incident upon the first optical element and thereby compensate for any changes in horizontal and vertical biases associated with a particular lithography device.
In an embodiment, the second optical element is made up of a set of lenslets. These lenslets can be arranged, for example, as a one-dimensional array of lenslets or as a two-dimensional array of lenslets. These lenslets can be replaced and/or repositioned in order to vary the angular distribution of electromagnetic energy incident upon the first optical element.
In an embodiment, a two-dimensional array of lenslets is formed from a plurality of one-dimensional arrays of lenslets. Each one-dimensional array of lenslets has different optical properties. Electromagnetic energy is passed through a particular one-dimension array of lenslets, selected from the plurality of one-dimensional arrays of lenslets, in order to produce electromagnetic energy having a particular angular distribution.
In an embodiment, each of the lenslets that makeup the two-dimensional array of lenslets can be individually selected and used to control the angular distribution of electromagnetic energy incident upon said second optical element.
In an embodiment, a coherence control module is used for selecting among the lenslets. A memory, coupled to the coherence control module, is used for storing data needed to select among the lenslets.
In another embodiment of the invention, the second optical element is a diffractive optic. This diffractive optic can be replaced by other diffractive optics having different optical properties in order to vary the angular distribution of incident electromagnetic energy.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.